(1) Field of the Invention
This invention relates generally to the field of DC-to-DC converters and relates more specifically to current limited DC-to-DC converters having multiple power sources.
(2) Description of the Prior Art
The performance of DC-to-DC converters is key for mobile electronic devices. DC-to-DC converters are often used to supply power for electronic devices as well as charging batteries at the same time if possible, i.e. if enough energy is available for both electronic devices and batteries. A limit to the input current of such DC-to-DC converters protects the power sources supplying the input for the DC-to-DC converter and the DC-to-DC converter itself and smoothes the output current of the converter.
Every modern integrated power management system has to be able to accommodate for a broad range of voltage sources (USB, 5V wall adapter, Firewire, automotive battery). Each of them comes in a variety of output specs, in particular regarding nominal output voltage and maximum current capability. The power management unit (PMU) has to guarantee that in every circumstance the load seen by the power source is within the specified ranges. This is generally done imposing a current limitation on the PMU according to the kind of power source connected to it.
Multiple power sources can be used to achieve a more stable operation of a DC-to-DC converter.
There are patents or patent publications dealing with the operation of DC-to-DC converters using multiple power sources.
U.S. Patent Application Publication (US 2007/0018502 to Bazinet) discloses a system for supplying power from multiple power sources to a powered device having first and second input power supplies for respectively providing power from first and second power sources. An input selector circuit is responsive to the first and second input power supplies for producing an input power supply signal provided to a power regulator, such as a DC-DC converter, for generating a regulated output power supply signal. The power regulator includes a first transistor device controlled to support conversion of the input power supply signal into the output power supply signal if the input power supply signal is provided by the first input power supply, and a second transistor device controlled to support conversion of the input power supply signal into the output power supply signal if the input power supply signal is provided by the second input power supply.
U.S. Pat. No. 7,132,764 to Kumar et al. proposes an apparatus and method for regulating multiple input voltages for a microelectronics device. The apparatus includes a controller configured to maintain each of the multiple input voltages supplied to one or more microelectronics devices within a range. The controller may be further configured to maintain input voltage according to a lower limit providing a wider regulation window for the power supply to operate without sacrificing performance for the microelectronics device or degrading its reliability. In one embodiment, the controller is configured to statically or dynamically adjust a gain factor for of a feedback loop in order to maintain the device input voltage according to a regulating loadline.
U.S. Pat. No. 6,522,190 to Malik et al. discloses a highly efficient power supply with redundant multiple input voltage sources. The power supply uses switching transistors, specifically MOSFET's, to create paths for current from one of the voltage sources to the load. The switching transistors are switched either “on” or “off” by comparators which compare the output from the voltage sources. These comparators allow the highest voltage source to provide power to the load, and keep the other switching transistors “off” that connect the common load to other voltage sources. Because the switching transistors have lower conduction losses than diodes in conventional power supplies, the power supply in accordance with the present invention is more efficient.